This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Characterization of the in vivo function of phosphatidylinositol 3-kinase (PI3K) signaling in theca and interstitial (TI) cells was our research focus in the past year of COBRE support. Theca cells are differentiated from ovarian interstitial cells. The major function of theca cells is to produce androgen for estrogen biosythesis and genomic action in granulosa cells. The principal disorder associated with theca cells is polycystic ovary syndrome (PCOS) in which an excess of androgen and other ovarian defects are often observed. However, the in vivo function of signaling pathway(s) key for androgen production in theca and interstitial (TI) cells in the ovary remains to be characterized, as well as the etiology of PCOS. Phosphatase and tensin homolog (Pten) is a negative regulator of PI3K signaling. Recent studies of Pten and other PI3K signaling molecules have shown that PI3K signaling (especially in the oocyte) plays a critical role in normal ovarian development and female fertility. However, the in vivo function of this signaling in TI cells remains to be characterized. To explore the function of PI3K signaling in TI cells in vivo, we have generated TI-cell specific Pten mutant (tPtenMT) mice. Increased phosphorylation of PI3K signaling downstream molecules such as 3-phosphoinositide-dependent protein kinase 1 (PDK1) and protein kinase B (AKTs) were observed in tPtenMT ovaries, indicating that deletion of Pten in TI cells causes an overactivation of PI3K signaling in the ovary. More importantly, premature loss of female fertility with aberrant estrous cycle and natural ovulation were observed in tPtenMT mice. These physiological defects in tPtenMT mice were due to abnormal ovarian development, as there existed a variety of histological defects in the ovary (e.g., ovary enlargement). Abnormalities displayed in tPtenMT ovaries should result from deletion of Pten in TI cells, and the primary defect should be in TI cells. To support this, androgen excess was observed in tPtenMT mice and elevated expression of Lhcgr and several steroidogenic enzyme genes key for androgen biosynthesis in tPtenMT ovaries and TI cells, as well as in luteinizing hormone (LH)-treated Pten-siRNA lentiviral knockdown TI cells. LHCGR is located on a recently identified PCOS susceptibility locus. Modulation of the LH and Lhcgr action in androgen production by PI3K signaling in TI cells could be an underlying etiology of certain types of PCOS. Consistent with this hypothesis, the abnormalities displayed in young adult tPtenMT mice mimic PCOS in humans. Like PCOS patients, tPtenMT mice were able to ovulate in response to gonadotropins. Moreover, API-2, a specific AKT inhibitor, was able to attenuate the ovary enlargement and the increase of ovary weight displayed in young adult tPtenMT mice. Together, our results suggest that Pten in TI cells is critical for normal ovarian development and female fertility and that overactivation of PI3K signaling in TI cells can lead to development of PCOS-like syndrome in young adulthood.